I personally love mine. I have a buggy rear setup on a 93 YJ with a 4cyl and a 4:1 T/C kit. My buggies springs are 17" long. That about as long as you can make on a YJ. CJ's I can't tell you too much about. There are some drawbacks. Shackle kickback can become a problem. If you are doing hardcore stuff (alot of dragging on rocks) it is possible to get the shackle jammed up. Particularly when the side with all the droop comes off a large rock. If the main spring drags on that rock the spring can be pushed up creating a locked up shackle situation. The solution to that problem is a set of kickback shackles. Something with a bushing to prevent the shackle from rotating too far. Remember the kickback can happen in either up or down motion. So the shackle ends up looking like a square or parellelogram piece of steel. I don't find any other major drawbacks. Minor ones are: change in pinion angle, lower hanging shackle, slightly less axle locating control.
The obvious pluses are: The increased droop, Can use a softer spring to gain same height as a stiffer spring, don't need long shackles(like those necessary for deep arch springs), increased compression. YUP, I said increased compression. If one side of the axle extends downward more and the opposite side is compressed all the way to the bumpstop, the compressed sides tire will be higher up in the wheel well. If you didn't get that, imagine a seesaw. If one side goes down the other will go up. The pivot of the seesaw being the bumpstop. Ofcourse, the correlation of increased drop to compression is not 1:1. It would be more like 4" more drop will give you 1" more compression.
One thing I didn't touch on is the driveshaft. There needs to be enough slip yoke travel for this to work well. The axle when at full tilt will probably end up pushing the driveshaft into the T/C more than before. One last note. Don't use aluminum axles shims. The axle will be pivoting back and forth on the center pin of the springs. Under extreme cases the back and forth motion will crack apart the aluminum. I would suggest steel. At the very, least do not use Superlifts CAST aluminum. I broke apart a set. If you're not using shims great. Might I suggest some grease or some other type of non friction material between the spring and spring perch.
Confused now? Hope it helps in your decision.
